1. Field of the Invention
The present invention relates to a method for manufacturing a semiconductor substrate dedicated to a semiconductor device, an apparatus for manufacturing a semiconductor substrate dedicated to a semiconductor device, a method for manufacturing a semiconductor device, and an apparatus for manufacturing a semiconductor device. Particularly, the present invention relates to a technology for readily forming a gettering site having a certain shape within a short time.
Priority is claimed on Japanese Patent Application No. 2009-133180, filed Jun. 2, 2009, No. 2009-136024, filed Jun. 5, 2009, and No. 2009-136362, filed Jun. 5, 2009, the content of which is incorporated herein by reference.
2. Description of Related Art
Recently, as electronics such as mobile phones and digital video cameras have been remarkably miniaturized, semiconductor devices such as semiconductor memory integrated into the electronics are also being miniaturized. The semiconductor memory is manufactured by forming a device on one surface of a silicon substrate (silicon wafer) made of, for example, single-crystal silicon. In order to miniaturize the semiconductor memory, the silicon substrate is thinned by grinding the back surface of the silicon substrate after forming a device on a surface of the silicon substrate to provide a thickness of, for example, 50 μm.
In such a thinning process of the semiconductor device, heavy metals may be introduced into the silicon substrate. If impurities such as heavy metals are introduced into the silicon substrate, a device characteristic is remarkably degraded due to a generation of a leak current or the like. Therefore, it is important to suppress diffusion of heavy metals in the device formation area after thinning the silicon substrate.
A gettering technique is widely known in the art as a method for removing heavy metals from the silicon substrate. In this technique, heavy metals in the device formation area are removed by forming an area for trapping heavy metals, called a gettering site, on the silicon substrate, and collecting the heavy metals in the gettering site through an annealing treatment or the like.
As a method for forming the gettering site on the silicon substrate, for example, there has been known an IG (Intrinsic gettering) method in which oxygen precipitates are formed on the silicon substrate (e.g., Japanese Unexamined Patent Application, First Publication No. H6-338507), an EG (extrinsic gettering) method in which a gettering site such as a backside defect is formed on the back surface of the silicon substrate (e.g., Japanese Unexamined Patent Application, First Publication No. 2006-313922), and the like.
The IG method of the related art is performed as a pre-process before a device is formed on the silicon substrate and requires a heat treatment temperature greater than or equal to 600° C. in order to remove heavy metals distributed on the silicon substrate. However, most of the heat treatments performed after forming the device on the silicon substrate are performed at a temperature less than or equal to 400° C., and the heavy metals introduced in the thinning process after forming the device may not be sufficiently trapped.
As recent semiconductor devices are being made thinner, the silicon substrate is required to have a thickness less than or equal to 50 to 40 μm, or further 30 μm. In the thinning process of a silicon substrate having such a thickness level, since most of the gettering sinks formed on the silicon substrate are removed by grinding, a sufficient gettering capability is hardly obtained.
Meanwhile, a large diameter substrate such as 300 mm wafer which has recently been popularized is polished in both surfaces. Therefore, in the EG method in which the gettering site such as backside defect is formed on the back surface of the silicon wafer, it may be difficult to form the gettering sink on the back surface.